Process of improving the moldability and extrudability of solid olefin polymers



United States Patent PRocassoF mrrndvn io THE MOLDABILHTY ANDEXTRUDABILITY, 0F SULID OLEFIN POLYMERS V John N. Scott, Jr.,Bartlesville, Okla, assignor to Phillips Petroleum Company, acorporation of Delaware No Drawing. Filed July 15, 1960, Ser. No. 42,984

p 2 Claims. (Cl.260-94.9)

Ths invention relates tomoldable compositions and method for preparingsaid compositions. In one aspect the invention relates to moldablecompositions prepared by heating high molecular weight polymers totemperatures below their softening points in an oxygen-containingvatmosphere. In another aspect the invention relates to a process forpreparing moldable compositions from olefin polymers having a molecularweight of at least about 75,000 by heating said polymers to temperaturesbelow their softening points in the presence of an oxygen-containinggas.

This application is a continuation-in-part of my copending applicationSerial No. 661,008, filed May 23, 1957, now abandoned.

As used herein the term olefin polymer is intended to include bothhomopolymers and copolymers of 'olefins.

Ethylene, propylene and higher l-olefins can be polymerized to"formpolymers having molecular weights of 150,000 or higher. For example,ethylene and mixtures of ethylene and other olefins can be polymerizedin the presence of a chromium oxide catalyst containing hexavalentchromium, and a liquid hydrocarbon diluent to form products havingmolecular weightsas high as 148,- 000 or higher. I v

While the high molecular weight polymers possess considerable utility,it has been found that as their molecular weights increase the polymersbecome more difiicult to mold. For example, when the polymer molecularweight exceeds about 75,000 conventional injection molding and extrudingbecome difficult.

It is an object of this invention to provide improved moldablecomposition from high molecular weight olefin polymers.

Another object of this invention is to provide moldable polymercompositions from olefin polymers having molecular weights not less thanabout 75,000.

Still another object of this invention is to providemoldablecompositions from polymers of l-olefins having a maximum of8'carbon atoms per molecule and no branching nearer the double bond thanthe 4-position, said polymers having molecular weights not less thanabout Yet another object of this invention is to provide a process forpreparing moldable compositions from high molecular weight olefinpolymers.

. These and other objects of the invention will become more readilyapparent from the following detailed description and discussion.

. In the broad aspect the compositions of this invention comprisemoldable compositions prepared by heating normally solid olefin polymershaving molecular weights of at least about 75,000 in' the presence of anoxygen-containing gas to a temperature below their softening points fora suflicient period of time to improve the moldability and extrudabilityof said polymer.

In another aspect the polymers are heated for a sulficient period oftime to provide a moldable composition having a high load melt index ofat least about 0.1, preferably a low load melt index of at least 0.5.

The polymers which form the starting materials in the preparation of thecompositions of this invention include a wide variety of olefinpolymers, such as, for example, polymers or copolymers of monoolefinslike ethylene, propylene, butenes, pentenes, etc. The invention isparticularly applicable to polymers of lolefins having a maximum of 8carbon atoms per molecule and no branching nearer the double bondthanthe 4-position. The starting materials can comprise high molecularweight polymers prepared by contacting an olefin feed with'a chromiumoxide catalyst containing hexavalent chromium and associated with atleast one supporting material selected from the group consisting ofsilica,'alumina, zirconia and thoria, and a liquid hydrocarbon diluentmaterial at a temperature of between about 150 and about 250 F. Thecatalyst employed was originallydisclosed in the patent of Hogan andBanks, Patent No. 2,825,721, issued March 4, 1958, and catalystdetails,including the methods of preparation, etc., are fully'disclosedin thatapplication. 1

In the preparation of the high molecular weight polymers an olefin suchas ethylene is contacted in'a reaction zone with the aforementionedchromium oxide catalyst in a liquid selected from the group consistingof parafiinic and naphthenic hydrocarbons. The contacting occurs at atemperature in the range of 150 to 230 F. when the liquid hydrocarbon isa parafiin and at a temperature in the range of 150 to 190 F. when theliquid hydrocarbon is a naphthenic hydrocarbon. Following the reaction amixture of liquid hydrocarbon and polymer is removed from the reactionzone and the polymer is recovered from the mixture. I v

The liquid hydrocarbon referred to serves as an inert diluent and alsoas a heat transfer medium in the reaction. While the liquid hydrocarbonis a solvent for the ethylene feed it does not dissolve the polymer atthe temperature at which polymerization is carried out. Thus, thepolymer product precipitates from the liquid in the form of smallparticles which contain the catalyst, from which the polymer can beseparated if so desired in subsequent processing steps. In general,hydrocarbons which can be used in the process are those which are liquidand chemically inert under the reaction conditions. Among the'moreuseful hydrocarbons are parafiins having between about 3 and about 12carbon atoms per molecule such as for example propane, isobutane, normalpentane, isopentane, iso-.

octane, etc. and preferably those parafiins having 5 to 12 carbon atomsper molecule. Also useful in the polymerization reaction are alicylclichydrocarbons such as isohexane, methylcyclohexane, etc. It is alsowithin the scope of this method to utilize mixtures of p'araffins andalicyclic hydrocarbons as the reaction medium.

The chromium oxide catalyst employed in carrying out the reaction canrange in chromium oxide content from 0.1 to 10 or more'weight percent,e.g. up to about 50 percent or higher, usually 50 percent or less, butthe preferred range is from 2 to 6 weight percent, expressed aselemental chromium. A preferred nonchromium component is asilica-alumina composite containing a major proportion of silica and aminor proportion of alumina. While the method for preparing thesilica-alumina composite undoubtedly affects to some extent the catalystactivity, it appears that composites prepared by any of the prior artprocesses for preparing such catalytically active composites, e.g.,coprecipitation or impregnation, are operative for the process of thisinvention. Methods for the preparation and activation of this catalystare Patented Apr. 6, 1965 impregnation step is dried and then contactedfor a period ofseveral hours; at a temperature of from about 450 to 1500F.,-p'referablyfrom about 900 to about 1000" F.,* a

under non-reducing conditions, for example, with a stream ofsubstantially anhydrous (dew point preferably F.- or lower)oxygen-containing gas, such as air. A commercial microspheroidalsilica-alumina composite can also be advantageously used in thepreparation of the catalyst.

catalystJin a fluidized system. hydrocarbon diluent is employed and thepolymer is recovered in the dry state associatedwith the polymerizationcatalyst. Nonequivalentcatalystswhich can be (less desirably)employed-other than the chromium oxide catalyst are organo-metalliccompounds such'as triethylaluminum plus titanium tetrachloride, mixturesof ethylaluminum halides with titanium chlorides and the like; halidesof aG'roup IV metal, such as for exampletitanium tetrachloride,silicontetrabromide, zirconium, tetrachloride, tin tetrabromide, etc.,with one orv more free metals selectedfrom the group consisting ofsodium, potassium,

lithium,rrubidium, zinc, cadmiumyaluminum, etc.

20 to 30 hours. [The same poly mer ,when. heated at 265 F. however,requires only about 2 hours Correspondingly an olefinipolymer of about150,000 molecular '10 weight requires 55 to 60 hours at 210? F. and onlyabout The high molecular weight polymers can also .be prepared byothermethods'and'by the use of other catalysts. For example, thepolymers can ,be.prepared by utilizinga gas phase reaction whereintheolefin is passed as 21-: gas through, a stirred bed ofv catalyst orcontacted with. In such a process no 'The high'molecular weight olefinpolymers are charac.-:

- terizedby having very high melt'viscosities and ahighdegre'eofcrystallinity. The melt index of these polymers,

whichiis a function of their viscosity, is not readily measr Boththe'time and temperatureemployed aredependexit on the properties of thespecific high molecular weight polymer being treated. Thus,:for example,when an olefin polymer having a molecularv weight of about j 100,000isused as the startingyniaterial; with'a heating temperature; ofabouti2l0 F.,"the timerequired is about this invention can beacceleratedby the use ofzultraviolet,

lightin addition to heat.

The time required forcarryingfoutthe heating. operation also depends onthe; surface area of the high molecular weight polymen Polymers preparedby the aforedescribed methodsare characterizeduwhen' 'in'particle formby'having a very high porosityand'even large particles of the polymerhave a high sur'face-to-volume ratio- Thusthe inventioncan be carried-,1out'by'utilizing large polymer particles, of afsize as large as A" indiameter.

However, preferably the polymer particles size-is less than 1A6".

to an oxygen-containing-gas. 1 If afluidized technique is employed,.it'is desirable that :thepolymer particles be 1 more finely subdivided toprovide ,ade'quatefluidization.

urable by standard techniques and thus is designated as Zero. It hasbeen commonly supposedthatthese low melt index'polymers aredifficultly', moldable and extrudablein present conventional equipmentwhich are essentially limited to the, molding of thermoplastic materialshaving a high load melt index of at le'ast0.1 as determined by the useof the high load technique hereinafter described.

For low load melt index, the method. of ASTM a weightof 21,600 grams.

. In carrying out the invention in one aspect thereof, a highmolecularweight polymer such as a polymer of ethylene is heatedto atemperature'below' its softening point in the presence, of anoxygen-containing gas for a F.,. and this temperature'therefore sets anapproximate upper limitfor the heating operation when polyethylenes] aretreated. The maximum temperatures are often higher for: polymersofpropylene or 4 -methyl-1-pentene. The.

invention can be carried out at as low a temperature as 32 F.; however,practically, to provide the desired results within a reasonable periodof time, the heating. step is carried 'out at a' minimum temperature ofabout 150 A more preferred temperature range is from about 200 to 265 F.The-time required to effect'the conversion of the difficultly moldablehigh molecular weight polymers to polymers having improved moldabilityand extrudability can .vary from a few minutes to as high as severalhundred hour's, however, usually thetime required is between aboutlOminutes and "about 100 hours If thexmelt index is D rl238-52T is usedwith five'runs-being. run at 2-minute intervals, averaging the, fiveweights, discarding any values" which' deviate from the average by morethan 5 weight percent, .reaveraging and multiplying by :5-to obtain the;i amount. of extrudate in :10 minutes.

low, such as lessfthan" 1.0, thehigh load melt indexmay be obtained byASTMD-1238-57T (procedure 5) using 'ployed as the starting materials inthis invention have softening points which usually do not exceed about265 -By operating in accordance with the process of this inventioncompositionshaving a meltindex of'as high as 20 or more, can be preparedfrom high molecular weight polymers, having a molecular Weight of atleast about 75,000 and a substantially :zero '1ow;-1oa'd meltuindex. Anydesired levelof melt index-can be obtained by proper- 1yadjusting theconditions emplo'yedin. theaforedescribed corporates a minor amountofoxygenintothe polymer some peroxide groups are present in thefinallcomposition; To' prevent cross linking during heating andsubsequent fabrication-operations a suitable antioxidant'can beincorporated into the moldable compositions after the heating step.Examples of suitable antioxidants of-the free radical acceptor type areamines-such as N,N-diphenyl-para=phenylenediamine, substitutedphen'olssuch as 2,6-

dl-tertiary butyl-4-methylphenol, alphaandbeta conindendrols, reactionproducts "of substituted phenols such as the reaction product ofacetylene .with alkyl substitutedphenols, quinones, etc. i V I I Theprincipaladvantageof the moldable compositions of this invention lies intheir improved moldability as compared to the startingmaterials. fHowever, other advantages accrue, because of theminor amount'of oxygenwhich is introduced into the polymer. Thusthe composition'sf of thisinvention have increased;dyeability, in

7 for bringing about theoxidation of olefin polymers; however, the priorart processes have been devoted exclusive- 1y to the treatment ofpolymers resulting from high pressure type olefin polymerization." Theproperties of the high pressure polymers have been such that, oxidationof these materials has resulted in their degradation "to waxy materials,The compositions of-this invention, however, are solid nonwaxymaterialshaving very desirable proper- Conversion of the high molecularweight polymer can be carriedsout in a bed, .eitherfixedor fluidized, orby otherwise suitably'exposing the polymer.

ties of tensile strength, crystallinity, etc. as comparedto both thestarting materials employed and conventional olefin polymers of highmolecular weight. f

The following data are presented in illustration of a '6 at'atemperature reduction rate of 15 to 20 F. per minute to roomtemperature, cutting a pea-sized specimen therefrormand placing saidspecimen in a 50-ml. glass stoppered graduate. Carbon tetrachloride andspecific embodiment of the invention: 5 methyl cyclohexane are added tothe graduate from 1 burettes in proportion such that the specimen issuspended EXAMPLE. in the solution. During the addition at the liquidsthe A series of runs were made in which high molecular graduateis-shaken to secure thorough mixing. .When the weight, highlycrystalline ethylene polymer, prepared by a P t l p s the Specimen,Portlon the h i oxide catalyzed polymerization, was converted llqllld istransferred to a small test. tube and placed on to a 1 1 composition theplatform of a Westphal balance and the glass bob Ethylene waspolymerized in the presence of normal lowered thETQIIL W1th thetemperature shgwfl y the pentane and finely subdivided chromium oxidecatalyst thermometer m the p f f'n to 78 the comprising 5 percentchromium as chromiumvoxide com ance 1s ad uSted untilthe pointer is atzero. The value taining 2.2 percent hexavalent chromium supported onshown on the scale taken as the Speclfic gravity silica alumina (90/10).The catalyst was prepared by p e from method of Karrer Dams andimpregnating silicia alumina with chromium trioxide solutench, E h (f'96 (1930): tion followed by drying and activation in dry air at tem-Camed out by mellmg a samPl? of the Polymer peratures up to px forsevera1hours insert ng a thermocouple into the molten polymer and Theconditions prevailing during the polymerization allowmg t moltenpollfmer to w The t mreaction were as follows: peratureis recorded andis plotted on a chart versus t1me. 1 The crystalline freeze point is thefirst plateau in the POLYMERIZATION CONDITIONS time-versus-temperaturecurve. V Temperature o 210 (5) Method of De Coste, Malm an Wallden,Ind.-'& Pressure p s i a Chem Ethylene f d rate ft 3/h 35 p e of theabove p p p yme p Pentane 22] All. L3 in trays 1n a forced draft; ovenand maintained at 212 Catalyst concentration in reactor ..wt. percent0.68 for varying lengths, h h pamcles of Polymer Chromium content incatalyst 25 were approximately inch in diameter and were of a Polymerconcentration in reactor ..do 15.5 hlghly l nature After polymer l beenheated in air at 212 F. for various lengths of tune, the The polymerfrom the above process had the following melt index of the material wasdetermined. These results properties. are given below as Table I.

POLYMER PROPERTIES Test'Method I Ash, wt. percent 0. 64 Molecular weight(by Inherent Viscosity) 145, 000

min. pull), percent.

Method of Clash and Berg. Ind. &

Eng. Chem. 34, 1218 (1942).

('1) Ind. & Eng. Chem. 35, 1108 (19 43). The concept of molecular weightis more fully discussed in Hogan and Banks Patent No. 2,825,721, issuedMarch 4, 1958. Unless otherwise specified, the term molecular weigh asused herein means molecular weight based on inherent viscosity using theStaudinger equation (molecular weight=2.445 1O inherent viscosity).Inherent viscosity is determined by measuring the time required for afiltered solution of 0.1000 gram of the polymer in ml. of tetralin(measured at 75 F.) to run through the marked length on a size 50 (0.8to 3.0 centistokes) Ostwald-Fenske viscosimeter at a temperature of 130C., the viscosimeter being immersed in a thermostatically controlled oilbath, and measuring also the time required for an equal volume oftetralin containing no polymer to run through the same distance on thesame viscosimeter. The inherent viscosity is calculated by the followingformula:

wherein C==0.183 and V =time in seconds required for solution to runthrough viscosimeter divided by the corresponding time required for thepolymer-free tetralin,

both at 130 C.

(2) Density as used herein is determined by compression molding a slabof the polymer, cooling said molding Table 1 Hours at 212 F.

Low Load Melt Index 0.00 0.1002 0. 414 1.15

1 Test Method hereinbefore described.

The sample which had been maintained at 212 F. for

'57 hours in the presence of air was examined for physical properties.

PHYSICAL PROPERTIES Test Method Impact Strength, ft. lbs./inch-notch- 4.93 ASTM D-256-54T. Tensile Strength (Injection molded- 4, 874 ASTMD-638-52T.

20/min. pull), p.s.i. Elongation (Injection molded-20"l 31 mm. pull),percent.

ASTM D-638-52T.

composition; I I v a The converted polymer (heated for 57'hours at 212F. )'Was also examinedby infrared spectrum to determine contacting anethylene-containingffeed with a chromium' oxide; catalyst containing.he'xavale'nt chromium associatedwith at least-onematerial selected fromthe group consisting of-- silica-alumina, Vzircjonia and thoria atvatially zero low load melt index and being prepared by I temperatureofbetween about 150.and aboutr250 F, 1 its molecular structure. .Thesedata are given below and which comprises heating said polymer indiscrete finely compared with the data fromthe infrared spectrum of adivided format a temperature 'of-'.between ab out;150 F. high molecularweight highly crystalline ethylene polyand'the softening point ofsaidpolymer in the presence of rner prepared under polymerization conditionssimilantcr a imid consisting essentially of molecularioxygeri at subthose listed above. 5 v r stantially atmospheriopressure for betweenaboutilO i T able -ll.rlnfr dred analysis a i [Figures-are ingroups/1,000 carbonatoms] lermin al Trans-Um Vinyl Iln- Carbonyl Percentmethyl saturated saturated Groups Crystal- Groups Groups Groups llnity 7High molecular weight, t

highly crystalline ethylene'poly'mer- N heated for 57 hours at V t 212 F1.5 0.1 0.0 1-2 88 Similar high molecular weight; highly crystal lineethylene polymer t (unheatedy nu'n' 1.5 0. 1 0.8 0.0 91

V It is to be'noted that the' unsaturationand crystallinity 'min'ut'e'sand 'about'y'loflhours and recovering a moldable of the heated materialwas substantially'unchanged from composition to increase'the high loadmelt index of said the corresponding propertiestofunheated highmolecular polymer t0'at least0.1 Weightpolymer. The difierence incarbonyl, groups dei notes the amount of oxygen contained in the heatedcom- ",Referencesfilted y 3 1 16 poiiltion. h "d b -d th b t d v iUNITED STATES PATENTS avrngt us escri e e inven ion y provr 111g a v7 av j g specific example thereof it is to bejlnderstoodtthat no un- 2 5 eta1 due limitations or restrictions are to be drawn byreason 105 1-0/60 7T thereof and that many variations and modifications are f gi j z'fi-f-" -f-f i j i f Ofthmnvemlon V, 1 3,013,003 12/61 Maraglianoet a1.26093,7 v a v 1 v A, 1. Process for increasing the melt lndex of. apoly- 8/62 rcawthron et i'f 216,0 ethylene having a melt index not aboveabout 0.05 and OTHER'REEERENCES v Y highmoleclllar. Weght l i 40ModernPlastics 32 (August 1955 117-120 and 122., ullllmmly s e Saldpslyahylene dlscrete finely Rubber and Plastics A e- 36 (November {1955655. dlvided form 1n SOlld state With elemental oxygen at temvTolythenen (Redraw), Puhuby Biff? and Sons peratures In the rangebetween about and about (London) 1957 (pages 71 727 and x for asufficient period of -trme to lmprove the (Kresser) FUEL u Reinhold (Newmoldabihty and extrudability of said polyethylene. 45 1957 Pa e 63 v2.vA method 'for improving thetmoldability and exa b a 7 7 1trudabilityof a solid polymer of ethylene, said polymer J H SCHOFER,Primary Examiner; having difiicult moldability and extrudability and a Ii I V molecular Weight of at least about 75,000 and a substan- LIEBMANGASTON M C;ISFFI S 50 7 x i a

1. PROCESS FOR INCREASING THE MELT INDEX OF A POLYETHYLENE HAVING A MELTINDEX NOT ABOVE ABOUT 0.05 AND HAVING A HIGH MOLECULAR WEIGHT WHICHPROCESS COMPRISING UNIFORMLY CONTACTING SIAD POLYETHYLENE IN DISCRETEFINELY DIVIDED FORM IN SOLID STATE WITH ELEMENTAL OXYGEN AT TEMPERATURESIN THE RANGE BETWEEN ABOUT 100*C. AND ABOUT 130*C. FOR A SUFFICIENTPERIOD OF TIME TO IMPROVE THE MOLDABILITY AND EXTRUDABILITY OF SAIDPOLYETHYLENE.